1. Field of the invention
This invention relates to systems and methods for removing soluble iron from household drinking water by oxidation.
2. Related Art
Well water often contains large amounts of soluble iron, commonly in the form of ferrous bicarbonate, which make the water less desirable for normal household use. Exposure to the air causes the ferrous bicarbonate to chemically oxidize, resulting in the formation of insoluble ferric hydrates. (Ferric hydrates include various oxidized iron compounds such as ferric oxide and ferric hydroxide.) These ferric hydrates, if not filtered out, will deposit on bathroom and kitchen fixtures, clothes or other surfaces, and create stains which are not attractive and are difficult to remove. Additionally, both the soluble ferrous bicarbonates and the insoluble ferric hydrates make the water taste bad.
Several methods for removing soluble iron from water are known. All of these have disadvantages that the present invention overcomes.
One such conventional system involves the use of chlorine to oxidize the soluble iron. Once the iron is rendered insoluble through this chemical oxidation process, a mechanical filtration device is used to remove the resulting insoluble ferric hydrates. This solution possesses many drawbacks which make operation of the system difficult for the homeowner. For example, the system requires a chemical feeder in which chlorine bleach has to be regularly applied. Additionally, the mechanical filter element tends to become super-saturated with iron hydrates and requires periodic media replacement.
A second conventional method involves the use of a cation exchange resin. This method is difficult to operate because the resin used in such a system must be periodically regenerated by treatment with aqueous sodium chloride to restore the iron-removing capacity of the resin. If the resin is not periodically regenerated, system performance will seriously degrade. Furthermore, the resin must be replaced regularly--an expensive and non-trivial task generally only done by a qualified contractor.
A third conventional method involved the use of an oxidation filter media such as manganese green sand. This method had disadvantages similar to the chlorine method--periodic regeneration of the manganese green sand was required to maintain the iron oxidizing capabilities of the media. Thus, a homeowner must periodically treat the green sand with potassium permanganate or with sodium hypochlorite, a potentially hazardous task. Potassium permanganate is a toxic, flammable substance that can leave residual stains on surfaces such as skin and clothing.
A fourth conventional method of removing soluble iron from household water involves the application of oxygen into the water through an aeration apparatus which causes oxidation of the iron, such that the resulting insoluble iron can be removed through mechanical filtration means.
The present invention includes oxidation for iron removal. Other systems that use oxidation are those shown in U.S. Pat. No. 3,649,532 to McLean, U.S. Pat. No. 4,430,028 to Paterson, and U.S. Pat. No. 4,659,463 to Chandler et al.
In the McLean system, the well water is pumped by a common well pump through a venturi-type apparatus which entrains air into the water. This air laden water is then introduced directly into a filter tank. This tank is shown to be disposed with a pressure switch and a pressure gauge. However, the tank itself does not appear to be disposed with means to pressurize water independent of the pump. Thus, no intermediate pressure tank is used. In fact, a purpose of the McLean system, as stated, is the obviation of a separate pressure tank. The venturi apparatus is designed to introduce only enough air into the water to cause the iron contained in the water to change into a colloidal form. Thus, the air intake is limited so as not to immediately oxidize the iron contained in the water stream.
The water with the iron in colloidal form passes into a filter tank and through the filtration bed contained in the filter tank. This filtration bed slowly raises the pH of the water passing thereto, which causes oxidation to occur according to a table noted in the McLean patent. The filtration bed simultaneously filters the ferric hydrates and other impurities therefrom. The McLean patent shows an air inlet that must be closely controlled in order to cause transformation of the soluble iron into colloidal form, without immediately inducing oxidation of the soluble iron.
The McLean system also shows an automatic air release valve which is provided to permit excess air drawn through the air intake to escape. The McLean system further shows a filter tank having a mineral bed resting on a course gravel underbed. The preferred mineral is dolomite, which itself consists of calcium and magnesium carbonate. This mineral is primarily responsible for raising the pH so that oxidation occurs. Significant drawbacks are readily apparent in the McLean system. Because the system uses no pressure tank, the pump must operate whenever water service is required. This will tend to decrease the life of the pump and thereby require more frequent replacement.
It should be noted that the present inventor is not aware of any commercial use of this system or other systems having no pressure tank.
The Paterson iron removal system includes an air injector in the water line between a common well pump and a common pressure tank. In the Paterson system, the iron in ferrous bicarbonate form is intentionally colloidally precipitated which results in enhanced particle surface charges for the colloidal particles. Thereafter, the air laden water with the charged iron particles is passed through a media bed carrying an opposite charge to attract the iron particles. The iron particles then electrostatically cling to the filter media. Note that the entire media bed depth is utilized for this electrostatic removal of iron particles. The Paterson system requires the air injector to be carefully set to control the amount of air introduced into the water. It also requires a specialized media bed preconditioned at the factory to have the opposite charge to the iron particles leaving the air injector.
The Paterson system also has serious drawbacks. If an improper amount of air is injected into the water, premature oxidation may occur. This would tend to clog the media blend and thereby severely reduce performance.
The Chandler system removes contaminates from water by introducing as much air as possible into the water to oxidize and precipitate the contaminants therein. A venturi nozzle assembly is employed in the Chandler system to maximize air input into the water with no special controls, adjustments or settings of the venturi assembly being required. Like Paterson, this venturi nozzle is piped into the system between a common well pump and a common pressure tank. One embodiment of this venturi assembly has a water bypass means normally closed by a dual layer diaphragm that flexes to allow additional water to enter. The system also incorporates an air venting assembly which includes a top manifold with an outlet selectively operative to vent excessive air from the tank while maintaining system pressure.
The Paterson and Chandler systems have many other common disadvantages. Because the aeration devices are located between the pump and the pressure tank, the installation time is greater than a system which does not require the aeration device to be placed between the pump and the pressure tank. Also, because the aeration devices are piped in line upstream from the pressure tank, the iron begins to oxidize while it is in the pressure tank. This leaves a residue of ferric hydrates which tend to clog the pressure switch and the pressure gauge which are attached to the pressure tank. This results in increased maintenance and parts replacement costs. Additionally, the residue from the iron oxidation tends to coat the inside of the pressure tank and decrease the efficiency thereof.
The Chandler and Paterson systems were confined to such an aerator placement because conventional aerator devices require 50 PSI and 8 to 10 gallons per minute of water flow in order to draw an acceptable amount of air. Because the output of common pressure tanks is in the range of 30-50 PSI (nominal 40 PSI), conventional aerators function properly only if they are piped in line between the well pump and the pressure tank.
Other systems and methods which involve the removal of iron from water appear to be described in U.S. Pat. No. 1,900,214 to Zapffe, U.S. Pat. No. 2,237,882 to Lawlor, and U.S. Pat. No. 4,534,867 to Kreusch et al.